Lyft, the ride-sharing company known for the bright pink mustaches on its drivers' cars, is launching its budget-friendly carpool option in Denver, Philadelphia, San Diego, San Jose, Seattle and Newark, New Jersey, over the course of the week. The expansion brings the service to a total of 15 cities across the US.

"Lyft's mission is to make our communities better by bringing positive change to transportation -- Lyft Line is the heart of that movement," said Logan Green, Lyft co-founder and CEO, in a blog post Tuesday.

Unlike a traditional Lyft rides, Line connects passengers going in the same direction and lets them split the cost of a ride. Each passenger gets dropped off at their set destination, so the ride may take longer than a private ride. Uber, Lyft's main competitor, offers a similar carpool service called UberPool that's available in a handful of US and international cities.

Line makes up nearly 40 percent of total rides where the service is available, Lyft said.